The present invention generally relates to optical detection devices and lighting methods used in optical detection processes. More particularly, the present invention relates to an optical detection device in which recognition and detection of an object is carried out by irradiating a light beam onto the object, receiving a reflected light beam from the object using a camera such as a CCD to produce image data, and processing the image data, and a lighting method used for such an optical detection device.
Recently, a number of manufacturing processes are automated and, accordingly, a need for automated detection means of a product has been increased. In a process of manufacturing semiconductor elements, it becomes possible to carry out a control of wafers by recognizing an ID provided on the surface of each wafer using such automated detection means. Thus, yields of semiconductor elements may be increased and a production efficiency may be improved by analysis based on the information obtained. For this reason, the ID recognition techniques in the semiconductor manufacturing processes have become increasingly important.
When an examination (recognition process) of an object is performed in a conventional manner, using image processing, as shown in FIGS. 1 and 2, a light beam from a light source device 1 is irradiated onto an object (in this case an ID 5 provided on a semiconductor wafer 4), a reflected light beam from the object is received by using a CCD 2, which is a camera means, to produce image data, and the image data is processed using an image processing apparatus 3.
There are two main lighting methods used in an optical detecting process--one is a coaxial lighting method shown in FIG. 1 in which a light beam is irradiated from the same axis as a camera axis and the other is a non-coaxial lighting method shown in FIG. 2 in which a light beam is irradiated diagonally. In the coaxial lighting method shown in FIG. 1, since the light source device 1 and the CCD 2 cannot be located at the same position, a half-mirror 6 is provided so that the axis of the light beam from the light source device 1 is superimposed with the axis of the CCD 2.
Usually, one of the above two lighting methods which is appropriate for examining an object is selected. This is because a better contrast or higher quality of an image suitable for an optical detection process may be obtained using one over the other. Also, both the coaxial and the non-coaxial lighting methods may be used at the same time for image processing on some occasions.
When the recognition of the ID 5 provided on the semiconductor wafer 4 is performed, both the coaxial and the non-coaxial lighting methods shown in FIGS. 1 and 2, respectively, may be used. Note that the ID 5 is formed before circuits are fabricated on the wafer 4. Also, the ID 5 is practically formed by shaving the surface of the wafer 4 using a laser beam. Thus, the ID 5 has a groove shape, and hence may be recognized optically.
However, when an examination is conducted on objects of varying shape in the above-mentioned optical detection process, since the shape of the objects varies, it is necessary to irradiate a light beam from various directions. In such a case, it is necessary to carry out irradiation operations of a light beam from various directions and select the best lighting mode.
In the above-mentioned coaxial and non-coaxial lighting methods or the combination thereof, however, the configuration of the lighting device tends to be complicated and the cost as well as the size of the optical detection device may be increased. Also, it is not possible to continuously change the irradiation angle of the light beam using the conventional non-coaxial lighting method (or device). That is, the irradiation angle must be changed using certain intervals (5.degree. interval, for instance). For this reason, the angles of the light irradiation which may be used are limited even if a plurality of non-coaxial lighting devices are employed. Hence, there is a danger that an optical detection process may not be performed under good conditions.
Also, when the ID 5 formed on the wafer 4 is detected using the system shown in FIGS. 1 and 2, it is necessary to carry out the detection process by irradiating a light beam from various directions by combining the coaxial and the non-coaxial systems since the structure of each ID 5 may be different depending on the method used for the ID 5 formation or the manufacturing process of semiconductors. However, if the irradiation angle of the light beam may not be varied continuously in the non-coaxial system, there is a danger that the best irradiating angle may not be used, and hence it is difficult to perform the light irradiation process for the ID 5 under the best conditions.
In order to solve the above-mentioned problem, the depth of the groove of the ID 5 formed on the wafer 4 may be deepened so that a larger contrast may be obtained from the reflective light. However, since an extremely fine process is performed in the wafer process, debris of the wafer from the groove portion after the irradiation of the laser beam affects the processes which follow. The deeper the depth of the groove portion, the larger the scale of the affection.
That is, the debris remains in the portion which is assigned to the circuit portion and causes problems. Thus, it is desirable that the depth of the groove of the ID 5 be as shallow as possible. However, a good image contrast is hard to obtain from the shallow groove using the conventional coaxial lighting system or non-coaxial lighting system, and hence it becomes difficult to accurately detect the ID 5.